如何从 DataGridView 读取 C# 中的单元格值

Question

im trying to do a StackAutomata for a School assigment and I try find the cells via for but they cannot read it int i, K and J is created outside the do {} while cicle

for (int j = 0; j < gv1.Columns.Count; j++)
                {
                    if (input[i].ToString() == gv1.Rows[0].Cells[j].Value)
                    {
                        K = j;
                    }
                }

                J = K;
                


string a = verem.Pop();
for (int j = 0; j < gv1.Rows.Count; j++)
                    {
                        if (a == gv1.Rows[j].Cells[0].Value)
                        {
                            K = j;
                        }
                    }

What am i missing?

Answer 1

It is seldom a good idea to directly read and write to the DataGridView yourself. It is better to separate your model from the way that your model is displayed.

If your data can exist without its display, it will be easier to change the way you display it, it will be easier to reuse the data in another control, or different format. Easier to unit test the data handling (no form needed,). to change the internal layout of the data without having to change those who display this data.

This separation between View and Model is implemented in extrema in the MVVM model, but windows Forms also supports this via Data Binding.

Whenever you have a control that displays information about a sequence of similar items, whether it is a ListBox, a DataGridView or even a GraphView, you'll find that it has a property DataSource .

All you have to do is put the data that you want to show in the DataSource. Other properties define how the data in the DataSource has to be displayed. If the operator changes the displayed data, then the original data is automatically updated.

Suppose your DataGridView has to show a collection of Customers: one Customer per row.

Your DataGridView has several DataGridViewColumns . Every column will show the value of one of the properties. The name of the property to show is in property DataGridViewColumn.DataPropertyName .

All you have to do is make a sequence of similar items, and assign this to DataGridView.DataSource.

An example will help.

Suppose you need to show a sequence of Students:

class Customer
{
    public int Id {get; set;}
    public string Name {get; set;}
    public DateTime BirthDay {get; set;}
    ...
}

You want to show these three Student properties in columns. Using the visual studio designer you add the columns and assign the DataPropertyName. The results can be found in InitializeComponents , or you can do it yourself:

private readonly DataGridViewColumn columnId = new DataGridViewColumn();
private readonly DataGridViewColumn columnName = new DataGridViewColumn();
private readonly DataGridViewColumn columnBirthDay = new DataGridViewColumn();

// constructor
public MyForm()
{
    InitializeComponents();

    // define which column should display which Student property
    this.columnId.DataPropertyName = nameof(Student.Id);
    this.columnName.DataPropertyName = nameof(Student.Name);
    this.columnBirthDay.DataPropertyName = nameof(Student.BirthDay);

    // the the DataGridView to use these columns:
    this.dataGridView1.Columns.Add(this.columnId);
    this.dataGridView1.Columns.Add(this.columnName);
    this.dataGridView1.Columns.Add(this.columnBirthday);
}

Usually you set other column properties: you set the text of the Header, the column order, sometimes you define the display format, for instance: for the Birthday you don't want to show the time of day. But if you want, you can make column Id readonly, with a bold font, etc.

Notice, that until now we have done everything without one actual Student.

If you want to display the Students but don't want to edit them, it is enough to put them in a Collection and assign this collection to the DataSource of the DataGridView

List<Student> students = ...
this.DataGridView1.DataSource = students;

However, if you want that operators can Add / Remove / Change / Reorder Students, you need a mechanism that the changes are updated in your students collection. This is done automatically if you put your data in a BindingList

IList<Student> students = ...
BindingList<Student> displayedStudents = new BindingList<Student>(students);
this.DataGridView1.DataSource = displayedStudents;

All students are displayed. The operator can Add / Remove / Change the Students as he likes (apart from the columns that you made readonly). All changes are automatically updated in the BindingList.

You can subscribe to events off the BndingList to react on these changes, but a more common scenario is that you do nothing until the operator tells you that he finished changing, for instance by pressing a button:

private void ButtonOk_Clicked(object sender, ...)
{
    DataGridView dataGridView = (DataGridView)sender;
    BindingList<Student> students = (BindingList<Student>)dataGridView.DataSource;

    foreach (Student student in students)
    {
         this.ProcessStudent(student);
    }

If you have saved copies of the original students, you can detect which Student are changed, added, removed and decide what to do with them. If you need to do something with the selected rows:

IEnumerable<Student> selectedStudents = this.dataGridView1.SelectedRows
    .Cast<DataGridViewRow>()
    .Select(row => row.DataBoundItem)
    .Cast<Student>();

One nice feature: suppose you want that your software assigns the Id of the Students, instead of the operator. Then whenever the operator wants to Add a new Row, you have to make the Student, with a unique Id. This is done by handling event BindingList.AddingNew

private void StudentCollection_AddingNew(object sender, AddingNewEventArgs e)
{
    // You need to make a Student with a unique Id:
    int newStudentId = this.CreateUniqueStudentId();
    e.NewObject = new Student
    {
        Id = newStudentId,
        // the operator has to fill in the rest of the properties
    }
}

Did you notice that you don't have to care about how the Students are displayed: you don't care which properties, what display format or column order. If in future someone decides not to show the Birthday of the Student anymore, or reorder the columns, maybe change show the name of the Student in capital letters: all these methods will still work.

Answer 2

for (int j = 0; j < gv1.Columns.Count; j++) {
  if (input[i].ToString() == gv1.Rows[0].Cells[j].Value.ToString()) {
    K = j;
  }
}

J = K;

string a = verem.Pop();
for (int j = 0; j < gv1.Rows.Count; j++) {
  if (a == gv1.Rows[j].Cells[0].Value.ToString()) {
    K = j;
  }
}

You cant compare gridview.Rows.Cells.Value with a string as it is an Object , just add the .ToString() Method and it should work.

Also please find a better name for your variables it makes your code more readable.